The present invention relates to a process for preparing a thin film magnetic head used for high density recording.
A general construction of a conventional thin film magnetic head is illustrated according to FIG. 2. A magnetic core 1 is made from a ferromagnetic thin film, such as Ni-Fe alloy (Permalloy), Fe-Al-Si alloy (Sendust) and the like. The magnetic core is composed of a lower core 1a and an upper core 1b to form a magnetic circuit. An insulation layer 2 made from SiO.sub.2, Si.sub.3 N.sub.4 and the like, is provided on the surfaces of the lower core 1a and upper core 1b which electrically insulate the magnetic core 1 from a lead 3. The lead 3 is made from an electroconductive material, such as Cu, Al etc., a part of which is inserted between the upper 1b and lower 1a magnetic core. The upper core 1b and the lower core 1a are assembled face to face to form a gap A and are magnetically connected at a back core B. A recording medium 4, such as a magnetic tape or a magnetic disc, addresses the magnetic core adjacent the gap 4.
In this type of thin film magnetic head, an important feature relating to head efficiency is the magnetic contact condition of the upper core 1b and the lower core 1a at the back core B. It is required that the lower core 1a of the back core B have no substances on the surface thereof and have a minimal surface roughness. In case these rquirements are not sufficiently satisfied, the reluctance increases at the back core B and magnetic flux will hardly flow in the core 1, which reduces recording and reproduction efficiency.
The conventional method for forming the back core B has deficiencies regarding the requirements mentioned above. The back core B is generally formed by etching the insulation layer 2 by way of photolithography to selectively treat the surface of the lower core 1a. There has been proposed many etching processes such as wet etching by a hydrofluoric acid containing etchant and plasma etching by a fluorohydrocarbon gas, among which reactive ion etching (RIE) by the fluorohydrocarbon gas is preferred. Because the thin film magnetic heads comprise a high density, i.e. are multichanneled, microfabrication techniques are required. On the other hand, while there have been proposed many materials for the core, such as Permealloy, Sendust, an amorphous alloy such as CoZr and ferrite, Sendust is preferred because of its high saturation magnetization, magnetic properties stability against a heat factor and excellent corrosion resistance. Accordingly, in the process for preparing thin film magnetic heads, it is preferred that Sendust be used as the core material and that the RIE etching process be adopted in the fabrication process of the back core.
However, the above process also has the following problems:
(1) A brown reaction product is produced on the Sendust lower core after etching the insulation layer by the RIE process. This product prevents developement of a clean surface, and PA1 (2) This reaction product, which is chemically inert, is removed with difficulty, because it is insoluble in water; organic solvents, such as acetone, xylene, ethylene alcohol and the like; acids, such as hydrochloric acid, nitric acid or sulfuric acid; and alkalis, such as NaOH, KOH. PA1 selectively etching the insulation layer from the surface of the lower core by a reactive ion etching (RIE) above or in a oxygen plasma to expose a part of the surface of the lower magnetic core, and PA1 allowing the etched article to stand in the oxygen plasma.
Thus, it is almost impossible for the reaction product formed on the surface of the RIE etched Sendust lower core 1a to be removed.